The Denver Museum of Nature & Science is leading the effort near Aspen. Officials there said Tuesday that more than 100 bones have been dug up so far this spring, including more remains of mastodons and three mammoth tusks.

A bulldozer operator discovered the first fossil at the site at the Ziegler Reservoir in October and many more Ice Age specimens were unearthed by scientists before the snow began to fall. The previous discoveries include remains of four Ice Age bison as well as mammoths and mastodons.

The museum says it’s one of the most significant fossil discoveries ever made in Colorado.